Apart form surrogate parameters like reduction of fasting and postprandial blood glucose levels or improvement of HbA1c, the effect of gliptins on micro- and macrovascular function and cardiovascular outcome has not been the primary focus of current studies. Diabetes mellitus is strongly associated with microangiopathy and macroangiopathy and is a strong independent risk factor for cardiovascular disease and cardiovascular mortality. Endothelial dysfunction which plays a crucial role in the atherosclerotic process is commonly observed in patients with diabetes mellitus and already prediabetes and has - amongst other factors - been linked to fasting and postprandial hyperglycemia. Taken into account that gliptins reduce hyperglycemia and hyperglycemic peaks by preventing inactivation of GLP-1, which exerted beneficial effects on the endothelium in previous studies it is of major interest whether therapy with gliptins improves endothelial function.